Antibiotic resistance is a result of intrinsic or adaptive genotypic and phenotypic responses of microbes that face compounds designed to be microbicidal. This problem is highly significant for the priority pathogen, methicillin-resistant Staphylococcus aureus (MRSA), which has emerged in healthcare as well as community settings. To meet this challenge, we are taking an innovative direction: discover and/or develop antibiotics that modulate microbes rather than kill them. Through innovative strategies and methods, and use of well-defined, quantifiable milestones our project leverages our exciting discovery that diflunisal (DIF) and phenyl-hydroxybenzoate (POHB) analogues thereof mitigate genotypic and phenotypic antibiotic resistance and virulence in MRSA. In turn, this effect enhances antibiotic efficacy in vitro and in vivo. Our Preliminary Data have already revealed potential virulence, resistance, and regulatory target genes modulated by these compounds. Importantly, compounds emerging as leads from our preliminary data are known via extensive clinical experience to be safe and well-tolerated in humans, and are FDA-approved. Moreover, we have already established an intellectual property position with respect to new and repurposed anti-MRSA uses of these compounds, a key to accelerating clinical development and commercialization. Our assay validation platform and program is knowledge-based and data-driven, thereby having a distinct advantage over more random and unfocused high throughput chemical library screens. Integration of an in vivo screen component will validate efficacy in the most prevalent (skin / soft tissue) and most difficult-to-treat (device-related) foms of MRSA infection. We will focus our initial program on MRSA as a proof-of-concept pathogen. However, our assay platform and concepts should be readily adaptable to target other MDR pathogens beyond the scope of this application. Thus, our plan drives innovative science, assay optimization and target validation, and efficient milestone-driven progress to identify lead candidates that restore or enhance efficacy of existing antibiotics, while mitigating emergence of resistance. Ultimately, results from this project are intended to accelerate pre-clinical and clinial studies of antibiotic-POHB combinations to improve treatment outcomes in life-threatening MRSA infections in humans. This strategy is highly attractive and immediately applies to a significant public health issue, affording a realistic bridge to the prohibitive time and cost of discovery and development of entirely new antibiotics de novo.